text:
How do you sump fuel when it's raining outside?
I've been taught to always sump the plane's fuel system before going flying to check for water / contamination / proper fuel grade. However, I've yet to go flying in rain. What's the proper procedure to drain fuel during rain? If I took the fuel cap off to dump the fuel back into the plane, I'd be worried about rainwater getting in the tanks.

I would suggest using an umbrella.

Is this considered a safe accepted practice? I'd be worried about wind blowing water into the tanks.

First of all, you really shouldn't be pouring sumped fuel back into the tanks. I suppose that is debatable. Secondly, the amount of rain that might blow into the fuel opening while holding an umbrella will be minimal and will not affect engine operation.

Originally when I did my training in Texas, I was taught to throw the fuel on the asphalt. By contrast, in the northeast, all of my instructors have told me the EPA would go after them for dumping fuel on the asphalt. I was taught to pour the fuel with through a strainer back into the tanks to filter out any contaminants, after verifying that no water was present.
I'd still be nervous about using an umbrella if it was raining really hard with strong gusty winds.

If its raining that hard, and that windy, you will most likely be delaying your flight until conditions improve. And again, a few drops that might make their way in while you quickly remove the cap, dump and replace will not affect engine operations.

Related (but not duplicate) question: http://aviation.stackexchange.com/q/1141/520

I hope that you are taking the fuel caps off as part of your preflight whether or not you are putting the sumped fuel back into it.  In a small airplane it's a very easy way to verify the amount of fuel on board the aircraft before you take it into the air.

@Lnafziger How do you check the fuel level if it's raining / windy outside? Umbrella?

@mike The same way that I always do.  Unless it is a monsoon (in which case you probably won't get a very good preflight in anyway), not very much water will be able to make it in.  If it is raining exceptionally hard, I would either wait for it to stop raining or do the preflight in a hangar.

AOPA has a good article about checking fuel:

... check the fuel caps and replace worn, brittle, or cracked seals
  that can allow rain to seep into the tanks.

You cannot be 100% that the fuel does not contain any contamination. If you risk that by putting the sample fuel back in the airplane (debatable topic) will add more water in the tanks, then simply don't do it.
I guess since many flight schools offer wet rentals, they don't want to waste a drop of fuel. But it is okay to do that, so that their aircraft and your life are safer.
Update
There are many arguments about putting sump fuel back in the tank. Many people say that a GATS Jar is there to capture the contamination and then you can put it back in the fuel tank. In Cessna training material, they use a container where you can put sump fuel. At many places, there is a fine for throwing it on the ground.
So in case of rain, the best option is to put in such a container. However, if it is raining that hard with strong gusty winds, I am sure taking care of sump fuel should not be your problem.

If not back in the tanks, what's the general consensus on where to put the fuel? Is it common practice to dump it on the asphalt, down a drain, or dump it in a container the FBO provides to safely dispose of it?

@Mike: See http://aviation.stackexchange.com/q/1141/520

This doesn't appear to answer the question about water getting in when the caps are removed during the preflight....


text:
Why do I get that funny stomach drop feeling right after takeoff?
Right after take off 1-2 minutes into flight I get this stomach drop "roller coaster" feeling for split second.  It freaks people out thinking they are about to crash!  Why is that??

It is your body interpreting unfamiliar accelerations.

Avoid a heavy meal before a flight.

Something like that also happens when you go down in a fast elevator because of inertia.

Your stomach is an accelerometer, just like your ears are barometers, your skin is a thermometer, your nose (might be) a weak compass, etc.

It happens when the airplane levels off after takeoff, usually either at the first assigned altitude or at a safe altitude where it will be accelerated in order to retract the flaps.   The feeling is a result of negative vertical acceleration.  It can also happen at other times during the flight, such as during turbulence or when starting a descent.
Basically you and the airplane are both in a steady climb and when the aircraft levels off you continue to move up faster so it (via the seatbelt) keeps you at its same level and decelerates your own personal vertical climb.
It is just like the feeling you get in a roller coaster.
My wife calls it a wee-hill!  :-)

EDIT:
Another more familiar example happens anytime that you are traveling in a car:
If you are in a car moving at a constant speed (let's say 55 MPH) you are moving at the same speed along with it.
When the brakes of the car are engaged, they slow the car down but your inertia tends to keep you moving in the direction that the car was going.  This will be more noticeable as the brakes are applied harder and harder because the deceleration of the car is more extreme.
You will notice this as pressure against the seat belt as the car holds you in place.  You are still moving forward, but you are getting slower (decelerating).  In an airplane the exact same thing is happening only it is in a vertical direction instead of a horizontal direction like in the car.
What you are feeling is your stomach floating up a little inside your body, because while the seat belt is holding you down, it doesn't hold your stomach in place!

Why isn't it possible to make this transition less sudden, making it barely unnoticeable for the passengers?

@Speldosa It is!  Much like in a car, the more abrupt the level off, the stronger the feeling.  It is very much dependant on pilot/autopilot technique and you will notice differences from flight to flight.

"It happens when the airplane levels off after takeoff, usually either at the first assigned altitude or at a safe altitude where it will be accelerated in order to retract the flaps." - I don't quite understand what you mean here.

You're saying that this happens when the airplane levels off, but you're also saying that it is "negative vertical acceleration" (i.e, falling). I'm so confused right now ;(

@Speldosa Negative vertical acceleration doesn't mean that you are falling.  Initially, you are in a steady climb (acceleration is 0 even though you are climbing). Then, as it starts to level, the climb starts reducing so you get negative acceleration until you level off and are no longer climbing.  Then the acceleration again becomes 0.

@Speldosa The airplane has to speed up before the flaps are brought up (retracted) so they typically level off in order to speed up.  Once they are going fast enough, they retract them!

@Lnafziger A better "car equivalent" would be quick levelling after a steep hill, IMHO.

@Speldosa - it is possible, but some airports have specific departures that require higher climb rates and more strict altitude requirements which can make it difficult to be more smooth.

This question is about 1 year old and already has good answers.
However, I like to track my flights with the GPS module of my mobile, which also records altitude. I'd like to share the data of a short haul flight, which also shows the effect:

After takeoff at 1:00, the first "funny-stomach-drop" occured after just 1 minute and 500m above ground, another at 5:00 and 3500m.
It is as said, the aircraft did not fall all the time. The climb rate just decreased to a lower, still positive value for a moment. This causes the same feeling like an upwards moving elevator, which stops at a certain floor.

Remember that GPS being on in the cabin is generally frowned upon (it's a "radio receiver").

It depends. Due to new regulations, electronic devices are allowed to be switched on "from gate to gate" on some flights (depending on carrier / aircraft). Any transmitters like bluetooth and wireless must be switched off, mobiles must be in "flight mode". As GPS is receiving only, it even works in flight mode. So, this is fine. It is really fun to see towns etc. through the window while a map on the mobile shows you their names etc. (I also once got a warning due to overspeed and a speed camera ahead...)

@sweber, what kind of phone do you have, and do you use a readily available GPS app? Or is this a custom thing you wrote yourself to log the data? This is something I've been wanting to do on training flights but I can't find a good app. (Perhaps because I have a windows phone.)

@elrobis: I've a Oneplus One (Android) and use OpenGpsTracker with fine (every second) position recording. The app can draw speed/altitude over time/distance, but can also export the collected data as GPX file (de-facto standard for such data). For this plot, I converted such a GPX file to a plain table using gpsbabel (linux tool) and draw the data using gnuplot. (Excel would be fine, too). But there are many apps out there which may be more suitable for you.

@elrobis: Another nice app: Mapfactor Navigator is a free navigation app (for cars) which allows to download maps from OpenStreetMap and use them offline. This is nice when exploring a country on vacation, as you don't need to take your car navi with you, and that navi may not know that country. This app also is nice in an aircraft to know where you are, what that city below you is etc. Unfortunately, it's not able to just record your current journey. And... switch off the speed camera warning. It's a bit odd when it claims that your 900km/h is a bit over the speed limit of the road below you.

Once in the climb, the flaps are retracted from the take off setting, the rate of climb reduces, then slowly increases again as the reduced drag allows the plane to go faster.

This is what I thought, and that's why I originally tagged this question with "flaps" tag but it was since modified

That's one possible cause of the feeling, but not the only one. (For example, in the light aircraft I fly you generally don't use flaps for takeoff, but we still reduce pitch and rate of climb once there's a safe distance between the plane and the ground. If I'm less-gentle-than-usual in doing that, or in leveling off for cruise, you'll still get that "floating" feeling.)

@KORD4me I removed the flap tag because the question,  even if the answer involved the flaps, is not about the flaps.  If the question were specifically about how the flaps affected this, then you would want to get the "flap experts" involved and the tag would be appropriate.

@Lnafziger, maybe this is not the right place, but how should we handle questions with multiple suspicions or sub questions?  For instance, would I need to create separate questions for each suspected "hunch" as the answer and tag them separately?  I tagged it with flaps specifically for flap experts to give their opinion.  Should I modify the original question to include more "hunches"?

@KORD4me If you had specifically asked in the question "Is this caused by the flaps" or something, then the flap tag would be appropriate!  :)

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
How does ATC protect Air Force One?
Air Force One is obviously a big deal.  We close terminals and implement other seemingly crazy safeguards against terrorist attacks while the president is en-route to an airport.
How does ATC protect the president whilst in the air?

I have heard of TFRs for "VIP in the area" reasons — is that for AF1?
I am guessing that the aircraft identification is blocked, but wouldn't they still need to have the transponder on for TCAS?

Specifically, the Wikipedia page on Air Force One has the following quote:

Air traffic controllers gave Air Force One an ominous warning that a passenger jet was close to Air Force One and was unresponsive to calls. "As we got over Gainesville, Fla., we got the word from Jacksonville Center. They said, 'Air Force One you have traffic behind you and basically above you that is descending into you, we are not in contact with them – they have shut their responder off.' And at that time it kind of led us to believe maybe someone was coming into us in Sarasota, they saw us take off, they just stayed high and are following us at this point. We had no idea what the capabilities of the terrorists were at that point."

Does having the transponder on just paint a huge target on the radar for terrorists?

Well primarily, ATC doesn't. I'm sure they'll vector aircraft away, but military F-16s are a much better protection

the time that Bush went to his troops in a covert mission AF1 adopted another call code and disguised itself as a smaller plane, but for most other applications any time the president is on board an airplane it automatically gets the AF1 call code (even if it is a tiny cessna). If the new president is making his oath and the old one is still flying then they'll need to request a new call code.

Aircraft are always an easy target because they are so delicate. At least when they are low to the ground anyway. As far as TFRs law-abiding pilots ATC tells us to turn left, we turn left. Terrorists don't obey laws so the TFR is kind of silly in that respect although I suppose it does help keep the number of overall radar 'targets' in the area down to a minimum.

ratchet freak, this is not quite true.  For example, when the President is on the Marine helicopters, the call sign is "Marine One".  the first word here indicates the "owner" of the aircraft:  Air Force, Navy, Marine, etc.  For a civilian owned aircraft, the call sign is "Executive One".

@SkipMiller I'd like to see what happens if the AF takes out a wet lease on an aircraft to transport the president. What would its callsign be? It's not an AF owned aircraft, but technically AF operated ;)

I'll accept 'operated' as a good substitute for 'owned'.  Thanks.

@SSumner, I used to vector traffic away from AF1, even if they were separated, if I would have to call traffic otherwise. I didn't like giving out position information on him, even if I didn't vote for him.  :)

Whenever Air Force 1 takes off or lands, the FAA establishes a 'Temporary Flight Restriction'.
Essentially this is a big 'upside down wedding cake' of airspace in which Air Traffic Control exercises very tight control of any aircraft operating in the TFR.  Any traffic entering the TFR without prior approval, or any aircraft deviating from ATC instructions will be intercepted by military aircraft.
When President Obama takes a bus trip the FAA establishes a TFR over the bus, that moves so as to stay over the bus as he rolls along!
Wikipedia has a good article on TFRs.

"upside down wedding cake" - Every presidential TFR I've seen is always to the surface.

Presidential TFRs are two cylinders, one is 10 nm in diameter and the outer is 30nm in diameter - both from ground level to Class A airspace (18,000 feet .)  The inner is Prohibited airspace and the outer is Restricted airspace.

TFRs over an area where the President is located don't move along with the President. If they did, neither ATC or pilots would know their location and that's no good. They know roughly where the President is going to be and put the TFR there and over a wide area around it (and this is usually announced days in advance where possible.) Also, as Mike said, VIP TFRs don't follow the "upside-down wedding cake" style structure like Class C/B airspace over a busy airport. They're just two concentric cylinders with each being from the surface to (but not including) the floor of Class A at 18,000 ft.

-1. The question specifically asks how ATC protects AF1 while it is airborne. The TFR does not exist when AF1 is airborne. A better answer would describe ATC procedures which could, for example, provide additional separation beyond the standard 1000 feet and 3 (or 5) NM provided to all other IFR aircraft.

Regarding TFRs, compliant pilots and terrorists: The TFR can "weed out" non-threats based on their compliance. Non-compliant aircraft would then be singled out as potential threats and dealt with accordingly. In addition, it doesn't just reduce the number of radar targets. It reduces the number of aircraft in the flight space concerned.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How should flaps be used during an emergency landing (PPL)?
I'm still doing my PPL, but one question has puzzled me recently. During an internal exam before my first solo nav on a C150, the examiner pulled the throttle, so I would do a simulated emergency landing. I chose a field right to me, and with a good gliding speed and without any flaps did a 180 turn (base+final) and found myself flying straight into power lines before the field. We had to go around.
The examiner showed me how it should be done. After the base turn, he deployed flaps 10 and then on final 20. We flew way above the power lines. Now I'm not sure all the altitudes and turning points were the same, but he meant this to show me that I should have used flaps.
My understanding had always been that the use of flaps during emergency landing should be restricted to the final leg from the point that you are certain you will make the airfield. My instructor (not the examiner) had the same view and could not explain it to me.
Any idea?

Rotary pilot here so commenting to give you something to work on rather than answering.  I believe that dropping flaps steepens the descent, therefore giving you more obstacle clearance on final.

I was always taught that flaps in an emergency is "pilots discretion". Using flaps makes you have a steeper descent but they are high-drag and could cause you to land short. Landing without flaps causes a longer roll-out but lets you "stretch the glide" a little bit. I also find it a little confusing how your DPE used flaps to clear an obstacle, there must have been some other factors. Maybe he did the downwind to base turn earlier?

Specifically in your case you may have lost more altitude in the turn than your instructor or your turns were less coordinated etc. A wide variety of other variables that are hard to note with out accurate course data could have led to your outcome. You would have had to enter the maneuver at the same place/altitude to get similar results and the wind would have an effect here as well. Did you have a head wind or tail wind? Its worth covering some general procedures for this maneuver.
When turning under glide its important to watch your airspeed and know how the plane will sink in a turn since you sacrifice some lift for the turn.
Remember flaps allow you to make a steeper approach with out gaining airspeed but what that also means is your ground speed is effected (slowed).
When it comes to the emergency landing procedure you are free to use flaps at your discretion and as mentioned its generally taught to use them once you are sure you have the field made. If the field is long enough you should shoot for a mid point incase you come up a bit short. Likewise if you are high you can go full flaps and slip it to lose altitude fast (if your instructor has not shown you how to slip a plane to lose altitude I would advise asking him to do so).


text:
During a touch and go (C150) should I first raise flaps or set full throttle?
I am now finishing my PPL (on a C150 in Czech Republic) and today had quite a close call when doing a solo touch-and-go on a short runway. We train on grass (and therefore rarely completely level) runways and take off with flaps 10 (landing with 20 or 30). I stayed in ground effect a couple of seconds before touchdown and then, according to my instructor's (hmm) instructions, first raised the flaps to 10 and then applied full throttle (and carb heat full cold).
I saw trees approaching and cleared them by an uncomfortably small margin (which made my further way back on which I managed to lose track a bit seem like a joke I wouldn't care about).
The explanation I heard from other flying guys is that touch-and-go should be an imitation of landing followed by a take-off, and one should therefore retract flaps (to 10) and then apply full power. And if you are not sure of runway distance left, you should make a full stop and take off anew.
Does this actually hold true? Imitation and practicing is all good and well, but assessing the runway distance left (and more so at an unfamiliar unlevel grass field I was landing at) in one second you might have may prove too risky and may lead to quite different consequences I was lucky to have avoided.
The instructor actually confirmed they were planning to change their route for the long nav flight because this field proved too challenging.
The question is, however, generic: first raise flaps or set full throttle?

If your wheels were on the ground, pull the flaps up first. If your wheels are not on the ground (go around), power first, then slowly flaps. The issue is that when you retract your flaps in the air you have a tendency to sink, doing it on the ground you can't sink so best to get in the take-off configuration before applying power. Honestly in this situation if you landed too long you should have immediately applied full power in ground effect and started a go-around. If your wheels don't hit at a target point on a short runway, go around.

It sounds more like an issue where you should have determined that you didn't have enough runway left for a touch and go, and either committed to a full stop landing or a go around (whichever could be done safely) prior to that point.  One good method is to choose a touchdown point while on final, and if it becomes clear that you won't touch down by that point then you should go around.  This will keep you out of similar problems in the future.  (As to your actual question, you may want to remove all of the extraneous details so that they don't cloud the issue.)

Thanks for your replies. Passed my checkride and got my license couple of days ago. Examiner put this very same question to me. And upon my answering that I would first retract flaps, said that on a short runway he would recommend to first give throttle. So now I think it's a matter of personal preference, at least in the way of looking at the whole touch-and-go process and objectives.

Flaps in a C150 (and pretty much any type) take a few seconds to move. Throttle change is more-or-less instantaneous. If you were to throttle up first, and then change the flap position there is a good chance that you are lifting off while the position of your flaps are changing. This is not a good idea, changing the amount of lift generated by the wings in this crucial stage of flight can lead to a take off stall. You could (and probably will) be too low to recover.
To minimise the chance of this happening, I would say that on touchdown, one of the first things I would do is to set flaps for takeoff ( giving the actuators a second or two to change flap position) before immediately setting take off throttle.
So, yes, your instructor was right. They usually are. In your specific case, I suspect that as soon as you floated too far down the runway, you should have initiated a go-around before touching down. You did not leave yourself enough runway to safely perform a touch-and-go. You dont assess take off distance available once you touch down, you asses it while still flying - you had ~10 seconds to make that call (approach, float, oh shit, go around!)

Throttle change is near instantaneous, but increase in airspeed (which is what gives the aircraft lift) is not. If you're close to, but not on the ground, it's much safer to go to max power, let the airspeed start climbing, and slowly retract flaps one notch at a time (or slowly, if you don't have notches). Removing flaps reduces drag, but also significantly reduces lift. If you're low, and you go remove flaps without gaining airspeed, you can slam into the ground.

@hashinclude I agree with you entirely - it is a matter of physics after all. This answer assumed you were actually on the ground.

One nit-pick: "Flaps in a C150 (and pretty much any type) take a few seconds to move." Pretty much any type with electric flaps. In planes with Johnson bar flaps (old Cessnas, many Piper models to this day) actuation can be nearly instantaneous as well.


text:
How should wake turbulence from aircraft on the ground be avoided during landing?
If a large jet aircraft is holding short of runway 28L while I am landing a single-engine aircraft on runway 28R, how should I proceed with such a landing?

It depends if the large jet aircraft is landing or taking off.

Some questions impacting your decision to land. Is the wind blowing from South? How distant are the runways? Have you been cleared for landing? Will the other a/c takeoff before you touch down? Are you IFR? Did ATC add a "Caution, wake turbulence" warning in the clearance? Can you touch down before being abeam the rotation point for the other a/c based on the relative positions of the thresholds? See FAA Pilot and ATC Guide to Wake Turbulence.

Wake turbulnce occurs when an aircraft is creating lift.  Since, the airliner is on the ground, there is no wake turbulence.
If you are worried about jet blast from the airliner holding short between the runways, then I would land past the airliner by about 1000 ft.  With the airliners engines at idle, there will be minimal jet blast but if the increase power that jet blast increases significantly.


text:
Do two of the same model of aircraft feel different to fly?
How does it feel when you change from an aircraft to another but of the same model?
Sometimes when you change a car and drive another one of exactly the same model you do feel differences due to various factors like wear and tear, mileage, different service schedules etc.
Does this apply also to aircraft or are they exactly the same?

If the airframe is the same it will fly nearly identical, especially if the motor is the same hp. Sometimes the switches move to a different spot or the avionics get more advanced but that is the kind of stuff you can practice on a simulator or sitting on the tarmac with a GPU hooked up, or have a qualified friend fly the plane while you sit right seat and play with the toys.

Note that fly-by-wire in normal law can mask such differences (an input leading to the same output)

The short answer is yes. I flew two different C152 in my flight school. One was very stable in level flight the other was not. One tended to glide very well in a power off situation and the other tended to sink. I made sure I stuck to one of the planes and that was the one I took my checkride in.

This applies to aircraft just as well as it does to cars.
There are little differences between aircraft from the moment they come of the production line, however these are barely observable. Over time the differences become larger.
For example, jet engine performance slowly deteriorates until the next overhaul, leading to increased fuel consumption. Another source of differences is permanent deformation of the aircraft due to extreme loads. A well known example of this is the B747 of China Airlines flight 006 that had a permanently bent wing.
In airlines flight crew sometimes know that specific airframes have specific characteristics like difficult lateral trim. The flight operations department will observe differences in fuel consumption between airframes of the same model. That can be a reason not to deploy a specific aircraft on long routes.
In addition to the wear and tear like causes there are design difference as well between airframes of the same model. This is described well by Terry.
A captain once told me she almost aborted an approach in IMC when the radar altimeter did not come up on final. It turned out the RAD ALT display was at a different position on the screen in this particular aircraft. Their fleet had several second hand aircraft with slight cockpit differences which caused confusion all the time.

"In airlines flight crew sometimes know that specific airframes have specific characteristics" -- yep, our most well known problem bird was ship 555, aka Christine, and every pilot who flew it knew it by that name.

In larger aircraft being flown by airlines that buy their airplanes from the carriers that originally bought them from the manufacturers, this can be a real problem. For example, Boeing used to allow considerable customization of 747 cockpits. For example, the forward cockpit overhead panel of 747-100 and -200 aircraft made for TWA had the switches reversed from all other purchasing airlines. The panel was at an angle, neither vertical nor horizontal. TWA treated it as a logically horizontal panel in that if you wanted a switch on, you moved it forward. All other airlines treated it as a logically vertical panel in that if you wanted a switch on, you moved it up. Thus, from the pilot's point of view, to turn on a switch on a TWA airplane, you moved the switch in the reverse direction of the other airplanes. Things got especially bad when switches from, say, an ex-Pan Am airplane were put in an ex-TWA airplane. Towards the end of my career (retired 1999), if I was in an ex-TWA airplane, I always looked directly at an overhead panel switch before throwing it. The differences section of the QRH (Quick Reference Handbook) of both 747 carriers I flew for was lengthy.
As I remember, the FAA finally stepped in and required Boeing to offer less cockpit customization.

The biggest differences that you will notice is that, especially on older models, the panel in the cockpit is not standardized and the avionics can vary wildly in both location and operation.  As an example, take a look at these two 172 panels:

Lighting is another thing that can vary from just barely passable to sleek modern solutions that allow you to see everything easily.
You should definetely take some time with any new airplane on the ground and learn where everything is before you take it up for an actual flight.
Aside from these differences, as others have pointed out, you may notice some small performance differences depending on the total time on the engine, etc.  These usually aren't that big of a difference as long as they are properly maintained.

haha - The 'lighting' part of this answer reminds me of my first night cross-country. Let's just say that this instrument panel's lighting was somewhat less than 'barely passable.' My CFI was wearing a head lamp, so there were quite a few instances of, "Hey, can you look over here for a second?" so that I could actually read the instruments.

A lot of this depends on what you mean by "the same model" - there is a lot more variation between aircraft than there is between cars, and a lot more that the pilot can customize. While every Ford Mustang you get in will be relatively similar even if you're going from mid-1960s to early 2000s models you could get in two planes that came off the assembly line right after each other yet seem completely different depending on what their owners have done to the avionics and airframe over the years.
On top of the avionics and panel layout and possible engine performance variation every aircraft is different: for the most part they're hand-assembled (even airliners to some extent) so there's variation there, and planes last a long time so each one has aged differently.
One airframe may have been in accidents and had major repairs that weren't quite to spec, another may have rigging issues (I flew a trainer that required left rudder in a right turn to remain coordinated), so you have to develop a feel for each plane you fly.

As another example of variation between planes consider that both Cessna and Piper have produced very long-lived "models": Cessna's 172 and Piper's Cherokee family (which I've picked because both are still in production today).
By one measure these are the same "model" (It's a Cessna 172, or a Piper PA28), and they'll fly largely the same as any other plane of the same type.
By another measure there are many different models in each family.
For example you could have a  Cessna 172 E with mechanical flaps, or a Cessna 172 F with electric flaps. You could have a Cherokee C model with "barn door" air vents and overhead trim, or an E model with the vents in the wing root and a trim wheel between the seats.
Sometimes these differences won't matter much to the pilot - the difference in air vent location in the Cherokees doesn't really affect your flying.  Other times it's a difference you need to be aware of, like whether your flap controls are a switch on the panel or a lever on the floor in the Cessna, or whether you reach up or down for trim in the Cherokee.

172's are a lot worse for this than people realize. I've found that the early models (I've flown a B, C, M, and P) are very sluggish with power changes (due to having a wildly different engine than the later models) and their landing flare doesn't look anything like newer 172's, which is the biggest issue for me. Newer 172s are obviously more powerful but they also seem a little lighter on the controls despite having a higher weight.
Anyway, my point is that I always tell people not to assume they know how a plane will fly just because they've flown the same model before.

The Swiss Air Force flew Hawker Hunters for three decades. Soon the pilots noticed that spin characteristics differed between individual aircraft. One would only spin in one direction, one would not get into a spin at all, and another would spin well left and right. The British never bothered to look deeper into this, but to the Swiss this was unacceptable.
Finally they found out that manufacturing tolerances made the nose gear doors close differently. On some aircraft, the left door would stick out a little more, on some it was the right door. Also the gap size was not identical between aircraft, and that determined the spin characteristics. Of course, soon all Swiss Hunters would spin identically.
I also remember that one Luftwaffe pilot told me that they would test fly their new Junkers 88s upon receiving them from the factory and found speed differences of maybe 20 km/h between individual aircraft from the same production batch. Then they proceeded to polish the normally matte paint of the fastest ones to have a super-fast plane for special missions.
Manufacturing tolerances might be small, but in some cases they can add up to produce noticeably different outcomes. Computerized and automated processes have drastically reduced those differences lately, however.

Engine performance and control rigging are probably two of the more obvious ways this is noticeable.
In aircraft with cable or pushrod controls, the system can develop slack and create a null zone where moving the controls does nothing.
As far as engines go, every engine wears differently. Some get crappy field overhauls and never really produce their original power again. Others are nearing end of life and have low compression in one or more cylinders.
Unless you're flying aircraft from an exceptionally well maintained fleet that distributes the flight hours fairly evenly, moving between models will almost always highlight a difference or two.


text:
PPL 40 hours requirement, are you really ready?
Are 40 hours of flight really enough to gain experience to fly a small private plane alone anywhere? The rules state so but from experience off you pilots, is it really enough or should be more hours be clocked with another experienced pilot next to you before venturing out?
Today I had my first flight on a 152 from Dar es Salaam International Airport, and the area is quite busy. There were bigger aircraft taking off and approaching and  many other taxiing.
Putting an inexperienced pilot that has barely 40 hours in an environment like this could cause serious problems even though he has gone through courses and exams. As you know one thing is theory and another is practice.
I would appreciate some clarification.

This is varies wildly from individual to individual, and would be pure opinion, so even if it's very well written question, I'll have to put in a close vote. People should have their personal limits, and not go places they're not able to handle. Same goes for everything in life, even if we're legally allowed to do something doesn't mean we should. You're legally allowed to go 300 mph on some German highways with a normal drivers license, doesn't mean you can handle it, perhaps resulting in the not-so-legal act of disrupting people around you.

OK. If it has to be closed no prob. Explanation is very clear.

Also keep in mind, you have to pass a checkride, it's not enough to have the required number of hours. You may have several hundred hours, and still not be allowed to go anywhere without an instructor signing off on it.

I went through the Air Force's Initial Flight Screening, and we   soloed after only 12 hours, and checked after 15-18. Now this did not give me a PPL, but most of us felt able to fly by ourselves out of a smaller airport. if we had had 40 hours, I feel sure we would have felt very confident. Now flying into a large congested area is very different, and like others have said just because you can do something doesn't mean you should.

That's interesting. in any case as from what I have understood from all your comments its just a matter of using brain! If you feel comfortable and ok go for it otherwise just let go. Thanks

@FabrizioMazzoni keep in mind 40 hours is the minimum time, and the majority of students take longer than that before they go for the checkride.  You won't be signed off for the ride and you certainly wont pass until you are ready.  It's your CFIs job to recognize that and the examiners job to verify it.

I think I solo'd in about 25 hours... then passed my checkride around 50 hours.   I could've done it faster, for sure.   I do think 40 hours is sufficient, subject to how the student approaches it.

One thing that was emphasized to me on the issuance of my PPL, is that it is a "License to Learn"  I took that to heart, and took it to mean that I was now in charge of managing my own risk as well as the complexity of situations I was comfortable with dealing with.  With a PPL, you can decide if you want to tackle a Bravo airspace, and when you want to complicate it with weather, and at a time with high traffic... or you may decide to get more comfy in your local Delta airspace first.

With the caveat that this is based on experience mostly in the US:
Most people take 60-80 hours to get their private pilot license:
http://www.aviationcareerguide.com/private_pilot_license.asp
The harder you work, and the more often you fly, the fewer hours you'll need.  The average hours are inflated somewhat by the many pilots who run out of time or money partway through, have to stop, and must then relearn what they forgot when they start back up again.  If you have the time, money, and dedication to fly two or three times a week, you'll get your license in fewer hours (not to mention fewer days!).
Don't worry too much about the safety of it though.  Your instructor won't let you take the exam, and your examiner won't pass you, if you're not ready.
As far as flying out of a major airport, my opinion is that it doesn't much affect the time or amount of experience required.  In the US, it's usually more expensive because costs are higher at large airports, but you may not have the option.  For most pilots, the hardest part of flying into a large airport is getting lost on the taxiways - but it will not take long to learn your way around your home airport.  If anything, it will make you a better pilot.  Today much of flying is dealing with controllers and airspace rules, and if you learn at a major airport, you'll have plenty of practice with that.


text:
Why does the landing gear control have 3 positions (up/down/off) on Boeing 737-800?
I've noticed that Boeing 737-800's cockpit has a 3-position landing gear lever. During takeoff, the pilot moves the lever from DOWN to UP and then to OFF position. What's the point of the OFF position? Why not simply have UP/DOWN positions?

Although the question asks about the 737, this setup is used on all "older" Boeing craft, back to the 707.

Just for complementing the Danny Beckett's answer: "In the event of turbulence the gear handle is selected back to UP to provide hydraulic up pressure to reduce structural loads on the mechanical uplocks." [Source: pprune.org/archive/index.php/t-351692.html]

@Claudix a number of people also replied saying they haven't heard of this before.

@DannyBeckett, yep, I just posted this comment to know what people from stackexchange thought about.

This arrangement can also be found on the 747.

L-1011 also had a third position, up/neutral/down.

When UP or DOWN is selected, the hydraulics pressurize in the appropriate direction.
Once the gear is up and the mechanical locks are keeping the gear locked in place, OFF can be selected to disconnect the hydraulic power.

Is it also true that you could move the lever to OFF with the landing gear in an intermediate position? Would there ever be a situation where you'd want to do this?

-1. this answer does not answer the question at all. It merely describes the operation. The question was what is the "point" of having an "off" position? Why did they build it that way? No other MFG seems to need it as they are all(mostly) either up or down only. It is easy for a system to  automatically sense up or down and not require pilot interaction for it so why did Boeing think differently on this particular model?

Why can OFF not be inferred by by UP? What would be a situation where you would want your landing gear to be UP but not OFF?

@SteveH, not limited to this particular model.  Is present on 707 and probably just continued to be used on models since (but not on 777).  I imagine folks didn't trust the "automatic sense" bit as much back in 707 days and just put it under pilot control.

If there was no off position the control system would be responsible for shutting down the hydraulic power when the gear reached its end stop. If there was a hydraulic leak, I'm guessing the gear would stop moving and the control system would pump all the hydraulic fluid out through the leak. Does anyone know if that circuit serves only the gear, or does it also serve more vital parts (like control surfaces)?

@LevelRiverSt: I don't know the precise hydraulic configuration of the 737NG, but, IIRC, airliners are required by the FAA to have at least three separate hydraulic circuits, with each hydraulic-actuated thing bypassed by at least one of the circuits, for exactly that reason (so that, if something hydraulically involved blows up or something, there will still be some hydraulics left).

With the gear handle in the UP position, the retraction side of the landing gear actuators remain pressurized. The gear will stay in the full up position, however they will not be hanging on the mechanical locks designed to hold them in the up position. They've simply hit the full up mechanical stop.
When the handle is placed in the OFF position, hydraulic pressure is removed from the retract side of the gear actuators, allowing the gear to settle down and onto the mechanical uplocks, which are essentially hooks that just hold the gear up.
There are a couple reasons why it's beneficial to select OFF. One is that if they remained pressurized, then the gear are essentially hanging in space, at a mechanical stop provided by the actuator. Hydraulic actuators are delicate components, and these weren't designed to hold landing gear for an extended time in the retracted position. Imagine the loads imposed on the actuator in turbulence for example, as the gear are loaded vertically with each bump. Removing hydraulic pressure allows the gear to hang on the mechanical uplocks that were specifically designed to hold them, without putting additional wear on the actuators.
The other reason is that gear actuators are major users of hydraulic fluid volume, and the actuators and the lines that supply them are a potential for leakage. If they were to remain pressurized for a several hours long flight, that increases the amount of pressurized lines and components that can leak and cause a complete loss of the hydraulic system.
Note that if you look at more recent Boeing airplanes such as the 777, 787, and 747-8, you will not see an OFF position on the gear handle, only DN and UP. The OFF function is done automatically on these models. After you select UP and the gear are all fully retracted, there's a short time delay and the system automatically depressurizes the retract side of the actuators. It removes one After Takeoff checklist item for the pilots to do.
To answer some of the questions posed in the comments:
If you selected OFF while the gear were still in transit in some intermediate position between up and down, they would simply freefall into the down position since you've removed the retraction power.
If there's a leak in the landing gear actuator or its associated hydraulic lines, it would cause a loss of that hydraulic system, and all other users of that system would be failed. The 737 has two (and a half) hydraulic systems. The half is a standby hydraulic system that's very limited in its function, but I digress.

I'm not sure it will "freefall". We are speaking of a significant weight whose abrupt displacement (freefall to from almost entirley up to down and lock position in less than few seconds) may be bad for flight control. I would think the design include drains such that if no power is applied, slow displacements of hydraulic fluid (and therefor displacement of gear retraction mechanism) and only those slow displacements are allowed. This way, gravity extension of landing gear may take several tenth of seconds but is smoother.

not too sure. it would decrease the chances of getting gears locked by the help of lateral movements in case of double hydraulics failure

If an actuator or hose let go, you wouldn't lose the whole associated hydraulic system. There are fuses that limit how much fluid you can lose through the gear actuation system. Now if you were to open a hole in the system upstream of the fuses, then maybe. As for manual extension; that takes several seconds from full up.

@ManuH: I thought that landing gear were specifically designed to be able to freefall, so that, if the gear hydraulics fail, the gear can still be locked in the extended position in preparation for landing by having it reach full extension forcefully enough to engage the latching mechanism?

@Sean I read somewhere (unable to find the reference now) that the pilot may shake the plane if the locking mechanism do not engage. Yet, there can be a good compromise between slow enough to avoid abrupt mass displacement and fast enough to engage locking mechanism.

The Mentour guy have a video, explaining the off position allows the wheels to freefall and be extracted manually in the case of hydraulics failure.
https://www.youtube.com/watch?v=aTS4BEKqi4U

I worked on the 737 Landing Gear system design in the 90s and can try and answer the question from memory.  All Boeing Commercial airfraft used mechanically positioned hydraulic selector valves until the 777, 787 and now the 737 NG starting about 3 years ago (now electrically commanded).  The cockpit handle drives a quadrant which drives a cable loop to a 3 position spool valve in the MG wheel well. So it can't be automatically depressurized by an electronic control system. Additionally there are several reasons to depressurize it in flight, although that question was heavily debated during the 777 system design.

The Nose Gear hydraulic pressure line which connects to the selector valve in the MG wheel well runs through the pressurized cabin compartment below decks. If it sprung a pin hole sized leak at high pressure it would eventually mist the cabin air making it uncomfortable to breath.  Skydrol is nasty stuff to get in your lungs.  Been there. So depressurizing it makes a leak less likely (in theory) and if it did leak at low pressure it would not form a mist.
The landing gear hydraulic supply is common to other flight control systems and so the hydraulic pressure droops from system fluctation would add fatigue cycles to the landing gear system if the valve remained in the UP position in flight.

On the other question; leaving the gear handle up in rough weather is news to me but there could be some airlines that chose to do so because the nose gear has a tendency to unlock in flight if it bounces hard enough.  It doesn't have an uplock hook but instead has a reinstating overcenter lock brace.  So I could see it being done.  Also, if both Main gears are deployed at full cruise and do not come back up, this is a big deal. On the Seattle Honolulu run, it would be a tough swim due to the drag fuel burn issue.
Note:  On the 777 there are two selector valves.  One for the nose and one for the main.  So the line running to the nose is pressurized in flight. Or at least it was when I worked the system in the early 90s.

Good info - thanks for adding a perspective that is new for even those of us who fly the 737's -- I'd never considered the idea of the line inside the pressurized cabin & the misting issue, though it makes complete sense as soon as you explain it. Welcome to Av.SE, and please check back often. The Boeing jets get a lot of discussion here, and the history you've seen will be a great addition to the board!


text:
How is the the turning error of an aircraft magnetic compass calculated?
I have a major exam in school tomorrow and I still don't get how to get the turning error of an aircraft magnetic compass. For example, if given an initial heading of 120 degrees and final heading of the Northern and Southern hemisphere, how to calculate the overshoot and the level off? I know the UNOS and ONUS but still don't get the concept of it. Please help me.

Do you mind if I ask what the exam is for? It's just it seems to me like you're after more precision than what is expected on the basic pilot exams.

Just made some little grammar edits for you. If I made a mistake with my fixes than you can change it back.

@Ben Agreed - in the UK we're just expected to be aware of it

First of all, in real life the overshoot will depend on the bank angle, so it is not really practical to do calculations unless you are doing some kind of special, precision flying or acrobatics. Normally you just get a feel for the overshoot and compensate intuitively. Exact calculations can be useful if you are doing precise figure-8's or something like that.
To actually do the calculation (which is based on a shallow turn 15-degrees to 20-degrees):
Target heading:
270 or 090 no correction necessary
northerly -- need to overshoot
southerly -- need to undershoot
Amount of correction (as variation from East/West parallel):
90-degree difference (eg heading 000) -- use 30-degree correction
60-degree difference (eg heading 330 or 030) -- use 20-degree correction
30-degree difference (eg heading 300 or 060) -- use 10-degree correction
Example 1:
You are on a 110 heading and want to turn to 030. You need a 20-degree overshoot. Turn left and roll out when you reach heading 010.
Example 2:
You are on a 335 heading and want to turn to 240. You need a 10-degree undershoot. Turn left and roll out when you reach heading 250.

The over/under on compass headings will also vary with the rate of turn, particularly in fluid-damped compasses (this is the real effect you're capturing when you describe "bank angle": you can have a slow turn in a 45-degree slip and a coordinated turn in a 5-10 degree bank with similar error characteristics).  The compass design also affects the error: Compasses with designs that promote eddy-current damping will have less pronounced overshoot/undershoot than ones without this effect.


text:
Is there any size of tethered kite that is regulated by the FAA?
Civilians fly kites for entertainment.
Is there a limit, after which the kite is considered an aircraft and becomes regulated?
Is a kite considered a balloon, after a certain size?  Do technology or other control apparatus make the distinction?  Is it purely height-based, and size is (mostly?) irrelevant?

Related

As one of my instructors was fond of pointing out, there's pretty much a regulation for everything -- in the US kites and balloons would be covered under FAR part 101 which is pretty short and to the point as far as government regulations go.
The big rules regarding kites/balloons kick in for a kite "over 5 pounds" or a balloon "over 6 feet in diameter / 115 cubic feet of gas capacity", and are:

You have to keep them at least 500 feet below any clouds.
You have to keep them less than 500 feet above the ground.
You must be at least 5 miles from the boundary of any airport.

If your kite/balloon is going to be more than 150 feet above the surface you're also supposed to coordinate with the closest ATC facility (who would theoretically put out a NOTAM saying "John Doe is going to be flying a kite/balloon/thingy here, between these hours. Please try not to hit it.")
There are also some lighting requirements (if you fly the balloon/kite at night), and visibility requirements (but really, who wants to fly a kite in less than 3 miles visibility? That seems like pretty lousy kite weather.)

As a favor to your local pilot community (and to prevent having your wayward kite dragged off by a Cessna on short final) it's probably best to observe the three "big rules" above regardless of the size of your kite - a 6-ounce piece of balsa and cellophane can still make a lot of people's days more interesting if it appears in an unexpected location.

This article mentions that the (former) Makani energy kite required an FAA temporary flight restriction in order to operate:  https://www.aopa.org/news-and-media/all-news/2019/january/23/new-airspace-obstructions-tax-faa-review-process

Also, since a kite is a tethered UAV, this stack-exchange question might be helpful: https://aviation.stackexchange.com/questions/27468/what-faa-rules-govern-tethered-outdoor-uav-flight


text:
How are aircraft size classes defined?
How come I see some large planes, such as the 747, classified as either Category 5 or 6 Gate Sizes, depending on the publication. Why do some sites count the plane as one size, while others state otherwise? Is there a definitive guide, or is it relative to the country/airport?

I cannot provide specific exmaples, however I do rember reading that an A380 was classified as a 5, and then later reading an A380 classified as a 6.

Is it possible that the change in category that you recall was from something early in the A380's development to later and the wingspan changed in that time period? (I have to admit, that a wingspan change of <65m to 80m is pretty unlikely, but it's a possibility, I suppose.)

I would believe that you are talking about Aircraft Design Group classification which is based off of aircraft wingspan and tail height. These classifications can also dictate what taxiways a certain model of airplane can use.

Group I: Wingspan - Less than 49' (15m)
Group II: Wingspan - Between 49' (15m) and 79' (24m)
Group III: Wingspan - Between 79' (24m)  and 118' (36m)
Group IV: Wingspan - Between 118' (36m) and 171' (52m)
Group V: Wingspan - Between 171' (52m)  and 214' (65m)
Group VI: Wingspan - Between 214' (65m)  and 262' (80m)

PDF for list of Boeing Airplane Group classifications


text:
What is the lowest allowable circuit height in Australia?
What is the lowest height an RPL holding pilot can conduct a circuit? I would like to practice very low circuits to work on my quick thinking.

That sounds like practising sticking your hand in the fire to work on your reflexes.

Yeah practice it at 6000ft and if you descend below that, consider yourself dead. Never practice using the ground. Frankly I think touch and go landings should be performed at FL150

Just remember, you can't beat the record for lowest flight -- you can only tie it.

I would suggest speak to an instructor about this sort of question...

I vote to close this as "primarily opinion-based". The answer from @RalphJ is very good, but I doubt you can find facts for this question.

Voting to reopen because the first sentence is a very clear question with an available answer that isn't opinion based. And I'm glad OP is asking instead of just going out and doing it!

@jklingler I'd say that Australia's aviation regulations count as facts.

You need to sit down with an instructor, rather than an internet message board, if you are seriously considering such a proposition as this.  Hopefully the instructor can talk you into a little more use of careful, cautious, wise thinking instead of a focus on what you term as "quick thinking".
There is a place for thinking quickly in aviation, but there is a much more important place for thinking wisely and avoiding unnecessary risks.  "How low can I fly this" doesn't very well fit into the category of wise & prudent.
I say this having in my background flying at lower altitudes for longer periods of time than most civilian pilots have been trained for.  Low level navigation at 300' was common in my previous role, but it was NEVER something that you got sent out to figure out by yourself.  You were trained to do it, how to do it well, and what to avoid.  And before each flight, there was some fairly extensive preparation, so that as many "split second" decisions as possible could be made well ahead of time, rather than on the spur of the moment.
I've also done some amount of flying (also in the military) where patterns are flown at 500' AGL.  Again, not something that is self-taught.  The big differences involve a lot of changes to the sight-picture, since you are now looking at the runway from an unfamiliar angle.  Can it be learned?  Yes.  Are there things that you need to be taught by people who have more experience than you do?  Absolutely.  Trying to do this on your own is a fairly good recipe for disaster.
Sit down with an instructor and have this conversation... Please don't do something foolish based on an answer from an internet forum!

First of all, I just want to reiterate that you should absolutely follow the advice in Ralph's answer. That is, learn to make good (wise, prudent) aeronautical decisions and talk to an actual instructor. Don't do risky things just to "practice quick thinking." That's how you end up dead.
Now, to actually answer the question regarding the lowest safe altitude, here's the regulation for Australia:

The LSALT (Lowest Safe ALTitude) must be calculated using the following method:

a. where the highest obstacle is more than 360FT above the height determined for terrain, the LSALT must be 1,000FT above the highest obstacle; or
b. where the highest obstacle is less than 360FT above the terrain, or there is no charted obstacle, the LSALT must be 1,360FT above the elevation determined for terrain; except that
c. where the elevation of the highest terrain or obstacle in the tolerance area is not above 500FT, the LSALT must not be less than 1,500FT.

Source: Aeronautical Information Publication Australia GEN 3.3 paragraph 4.5
So, in summary, the lowest safe altitude is 1,000 ft. above the highest obstacle, except that it must be not less than 1,360 ft. above the highest terrain and not less than 1,500 ft. above sea level.


text:
What could these possibly incorrectly translated numbers for aircraft speed have been?
Yesterday I was watching a show about Air Crash Investigation, the
Air France flight 447 case involving an Airbus A330-200.
I was watching it with Spanish voice dubbing and the weird part is that the narrator said the plane...

reached a final speed of 13,000 km/h
started falling at 7,000 km/h
crashed at 200 km/h

The only speed value that makes sense to me is the last one: 200 km/h.
My guess is that something was missed in translation. What is usually the speed measure for aircraft in the US?
I also thought about the 7,000 figure, and perhaps instead of speed in km/h it meant altitude in feet?

This could be in reference to vertical feet per minute that the aircraft was falling.

you mean vertical speed of 13,000 feet per min?

The last recorded vertical speed was 10912 ft/min = 199.6 km/h, so that matches the last value. Not sure what the others are referring to. Max altitude was 38,000 ft = 11582m, which doesn't quite match the first.

I think there is some information lost in translation.
The speeds of 13000 kmph are associated with reentry vehicles. The aircraft won't have had time to accelerate to that speeds in the first place, even if there is no atmosphere.
The (forward) speed is usually measured in mph in US (to the best of my knowledge). The vertical speed is given usually in feet per minute. Note that the aircraft speed is usually given in knots (or its Mach number) by convention.
Now, the numbers you've quoted:

7000 When the autopilot disconnected, the roll angle increased in two seconds from 0 to +8.4 degrees. In response, the Pilot Flying (PF) applied nose-up sidestick inputs, which the Investigation termed as abrupt and excessive. As a result, the aircraft started to climb at 7000 ft/min.
200 The (vertical) speed at impact was around 108 knots (10,912 ft/m), which is around 200 kmph.
13000 I'm not sure about this one. The maximum altitude reached was less than this value (~11500m actually), so doesn't make sense. The only thing that is related to this number for that flight was the depth at which the wreckage was found- 3,980 metres or 13,060 ft.

Note: Most of the data is from the Final accident report of Air France 447.

Thanks your answer at least answer two of three. I will give some chance and maybe someone watch that episode too.

I think I found it http://www.dailymotion.com/video/xz57px_mayday-air-crash-investigation-s12e13-vanished-air-france-flight-447-1080p-hd_shortfilms at min 33:30-33:50 say falling at 12,000 feet per minute


text:
Where is a missed approach point for circling while flying ILS?
In my company we have a problem that we cannot understand completely, because we  cannot find the answer.

If I don't have the runway in sight at the circle minimum (MDA) on an ILS
approach, I must immediately execute a missed approach or can I level off and maintain the circle minimum (MDA) and continue inbound until reach the MAPt by DME or timing block (don't have DME) and missed approach?
If a RVR is published in the chart, normally it is RVR at MAPt right? For ILS (precision approach) it is clear that MAP is at the DA. LOC (Non-precision approach) uses MDA at MAPt by DME or timing but for circling where is a MAPt? Use same Non-precision or use circle minimum (MDA) on glide?
If we fly ILS for circling, is it a precision or non precision approach?

Circling approaches are non-precision, regardless of how you arrive at the MDA.  When circling you'll level off at the circling MDA and use the missed approach point depicted for the approach.
If you are looking at a Jeppesen approach plate there should be a level-off and 'M' depicted in the profile view.  If you are looking at government plates the level-off and MAP are not depicted in the profile view but are still specified elsewhere.  In any case, you'll fly the localizer to the MAP and then go missed.  You'll descend either via the GS or step down altitudes to the circling  MDA and stay there until either the MAP or you are able to further descend.
RVR probably won't be listed for circling minimums (it isn't published for the chart as a whole) as they will generally be at least 1 mile or more.  Whether the visibility requirement is specified in feet (RVR) or miles, this is the visibility you need to descend out of the circling MDA.  You have the further restriction that you may not descend out of MDA until you are in a position to land.  The same familiar rules in 91.175 still apply.
In summary, fly the approach like you normally would but level off at the non-precision circling MDA and go missed at the non-precision MAP if you have no visual contact with the runway.  You do not go missed exactly upon reaching the MDA, just as you wouldn't if you were flying a VOR or LOC approach.  You go missed at the missed approach point.

Thanks you Casey Now I can understand completely, as you mentioned. But many people in my company does not believe that it is correct. They ask me for more references. Sir, please help me!! Where I can find more references ? to make them believe that your answer is correct.

@PoroSripaew if your coworkers don't understand the non-precision procedures represented by the e.g. S-LOC and Circling procedures in the above plate, I'd turn this around on them.  Get them to motivate their positions and refer them to the FSDO for a written interpretation if they aren't satisfied.

See FAA Instrument Flying Handbook 2012, especially pages 10-20 and 10-21 for some references. Available here link

@PoroSripaew And if you are flying in areas where procedures are not designed using US-TERPS but instead use ICAO PANS-OPS, refer to ICAO Flight Procedures (DOC 8168) - Arrival and Approach Procedures. In particular Section 7 - Visual Manoeuvring (circling) area.


text:
Can 'neutral static stability' only be achieved by constantly augmenting the control surfaces?
I watched a flight mechanics lecture that mentioned that some combat aircraft like the Hornet has a 'mode' where the on-board computer simultaneously and automatically adjusts all the control surfaces to make the plane fly with Statically neutral stability which to my understanding means that the lift moment is constantly aligned with the plane's center of gravity.
The result is that the pilot is able to pull back on the controls and pitch up and release the input and have the plane continue to fly in a new direction without any tendency to diverge or return to equilibrium (the trim position).
Is this true and is this stability only possible with a constant re-balance of the control surfaces of the plane?

Related: The 3 Types Of Static And Dynamic Aircraft Stability, also What does it mean for a plane to be aerodynamically stable? and Flight control surfaces.

First, definitions- The purpose of trimming to to free the pilot from having to exert a constant pressure on the controls i.e., when the aircraft has been trimmed, there is no need for the pilot (or autopilot) to give any control input (for a set of conditions like level flight or climb).
An aircraft which is (statically) neutrally stable tends to stay in its new attitude when it's disturbed. For example, if you pitch the nose up by, say $2^{\circ}$, and then immediately after that it stays at $2^{\circ}$ nose up.
As can be seen from above, you need not balance the control surfaces continuously while the aircraft has been trimmed. Stability has to do with the aircraft attitude and not control surface movement.
The aircraft (like F/A-18 Hornet) require constant operation of flight control surfaces (by computer) because they have relaxed static stability- they will oscillate and diverge from an attitude if left to themselves.

This is not as clear, to me, as it should be. So, a statically neutral stable aircraft, pitched up those 2degrees will stay at that new attitude, with no changes to the control surfaces, by either the pilot/autopilot or computer?

@CGCampbell That's correct. Positive static stability means it returns to the previous attitude, neutral static stability means it keeps the new attitude. This is an aerodynamic property. What aeroalias is saying is that the F/A 18 is NOT aerodynamically stable. It has a computer that automatically reacts to changes in order to make it possible for the pilot to control it. From what the op says, apparently the flight controls are programmed to mimic neutral stability.

Maybe @rhinodriver will confirm if that's how the F/A 18 is programmed

@TomMcW said it best: apparently the flight controls are programmed to mimic neutral stability. Well said!

I know this is old, but for the people who are still looking for information regarding this subject, this explanation is not complete and partially inaccurate.
First, there are 2 types of stability. Static stability and dynamic stability. It is true that stability comes from the current situation attitude (angle of attack), but it has different effects for different aircraft. And it is possible to have positive static stability but with dynamic instability. Case in point, 727's deep stall where it's attitude effectively locks the tail in a 'wind shadow.' It causes oscillating moments that don't exist outside of this flight profile.
Static stability has to do with the short period moments of the aircraft. An aircraft with positive static stability is said to have a forces acting to try and return the aircraft to trimmed flight at its trimmed alpha. A neutrally static aircraft will desire to hold the current alpha even after disturbed. An aircraft with relaxed static or unstable static stability will continue to increase its alpha in the direction opposite of the flight path. In other words, neutral static stability will not remain at 2 degrees of pitch attitude (theta) once the stick is released. Instead, it will maintain the pitch rate (theta dot) that it had when the stick was released. Static stability will never have a description of oscillating moments, instead it will describe what happens right here, right now if a momentary force acts upon the aircraft.
Dynamic stability is the stability of the aircraft in the long term. It describes what happens after a certain amount of time. A dynamically stable aircraft will have no or little oscillating moments and will dampen oscillations over time. It will follow a trend that is predictable. An aircraft with neutral dynamic stability will maintain its oscillations until acted upon, and then after, continue whatever oscillations remain. But an aircraft with negative dynamic stability will continue to have diverging oscillations, increasing in amplitude from its original orientation.

The following 9 conditions describe, by example, what will occur with static and dynamic stability are both taken into consideration:

Positive static stability with positive dynamic stability: Aircraft will immediately attempt to return to its trim condition and
will have oscillations that dampen out as the forces return to
equilibrium.

Neutral static stability with positive dynamic stability: Aircraft will hold its current alpha and its pitch rate will remain
constant with regard to its current alpha and the oscillations from
the disturbance will slowly dampen out and return to equillibrium.

Negative static stability with positive dynamic stability (bit of a misnomer, explained below):
Aircraft will continue to
increase alpha and its pitch rate will increase. The misnomer is that
there will be no oscillations because there are no forces acting to
return the aircraft to its previous state in the long term. So this
technically can't exist. Airspeed will continue to decrease and drag
will continue to increase until it is more of a brick than a plane.
This is undesirable in fighter aircraft as if it enters a spin, any oscillations that could help exit the spin will quickly
dampen out and recovery will be nearly impossible. (with regards to
the lateral axis only)

Positive static stability with neutral dynamic stability: Aircraft will want to return to normal flight, its AoA will decrease,
and its pitch rate will reverse. But the aircraft will continue this
oscillation indefinitely if no corrective measures are taken.

Neutral static stability with neutral dynamic stability: Aircraft will want to continue to maintain it's current angle of
attack and any disturbances and oscillations for correcting forces
will continue to oscillate as they did before. It have epitrochoidal
motion.

Negative static stability with neutral dynamic stability (yes, this exists, and is what is common in some fighter aircraft):
Without corrective inputs in a timely manner, this will have an
oscillating period and will also continue to diverge from normal flight. This can be a good thing when trying to recover a
fighter from a spin as the oscillations will continue and the aircraft can be "rocked out." The F-16's deep stall behavior is very much described like
this, and can be described as a falling leaf. I have a video on this,
from a simulator called DCS World, here. In fact, in the video, you can also see that the longitudinal axis also suffers from neutral dynamic stability in this flight envelope. The switch I press at 1 min and 45 seconds overrides the computers maximum control surface deflection window and I can then "rock the plane out" by increasing the amplitude of the oscillations until the airflow over the control surfaces allows the computer to recover from the deep stall.

Positive static stability with negative dynamic stability: This is what you want when you want to make passenger planes into
vomit planes. The corrective forces acting on the plane cause it to
overshoot and the oscillations increase in amplitude. But the plane
is still trying to right itself in the short term.

Neutral static stability with negative dynamic stability: At this point, I don't know if there is a point in describing the
behavior because I think you might be able to get the gist. The plane will want to maintain its current alpha, but will then reverse, causing larger amplitudes of oscillation on each reversal. It might have 1 or 2 cycles before it completely
diverges from controllable flight. Not the characteristics you really
want to have in an aircraft.

Negative static stability with negative dynamic stability: Just pure chaos. Basically any orientation along the lateral
axis will have a 'butterfly effect' response and unpredictable
behavior. Forces put in to try and correct it will have an
oscillatory response that will increase in amplitude on the next
cycle, causing the need for a larger input to correct and the pattern
repeats.

Currently studying flight dynamics as a hobbyist and with 2 years of engineering school. Current project is for model aircraft with a flight control computer to emulate an aircraft with negative static stability and neutral dynamic stability.
And, for references sake, so you can figure this out on your own in a sort of mental simulation:
https://www.boldmethod.com/learn-to-fly/aerodynamics/3-types-of-static-and-dynamic-stability-in-aircraft/

"pilot is able to pull back on the controls and pitch up and release the input and have the plane continue to fly in a new direction"

Thrust must be added to "continue to fly in the new direction" or else the aircraft will slow down and depart from straight line flight.
What happens next will depend on the directional stability of the aircraft.  Once the aircraft begins to curve downward, the change in relative wind will increase AOA over the entire aircraft.
This means non-lifting parts of the aircraft, such as the fuselage, can contribute to the "weathervaning effect".  As the nose drops, speed, and lift will increase.
So, with any computer-augmented control system, it might be a good idea to find out exactly what it does.  Computer control inputs should be the same as human ones, but computers are tireless and many times faster.
A change in static stability from positive to nuetral could be accomplished in flight with a shift in center of gravity by dropping ordinance or transferring fuel, but it might be easier to keep it neutral all the time and have different levels of autopilot.
Just "adjusting control surfaces" generally makes the plane pitch, roll, or yaw.


text:
How is a traffic pattern oriented, entered and exited?
If you've received traffic entry instructions from Heathrow Tower (sim) to fly left downwind for runway 9L, does that mean to be to the left of runway 9L (for a right-turning traffic pattern, where downwind is north of the runway) or to enter a left-turning traffic pattern? I ask because the latter would take you over runway 9R/27L and I'm unsure whether this is a problem or whether it's ok because of the difference in altitude between a plane in 9L's downwind and 9R's/27L's final/upwind.
Also, if you've received clearance from runway 9L to depart north, should the departure be done from the traffic pattern? E.g. you take-off, turn crosswind, turn downwind then turn base and depart the airspace? Or should you continue straight until you've left the airspace, then change course?

Why Heathrow?  This would never happen at Heathrow which does not have "standard" patterns.  All arrivals and depatures are via SIDs and STARs or vectors from ATC.

I should've added that a) this is a sim (which explains why the question might not make sense) and b) I'm quite new to aviation and only chose Heathrow because it's a familiar place. Would there be an answer if it were another airport with identical runways that did have standard patterns?

Left downwind means left-hand turns in the circuit, so you should pass with runway 09 on your left, travelling on heading 270 - then do a few left turns and you're on final. You don't cross over the other runway's flight path. (And yes, I appreciate you're asking about a simulation so you're not really flying visual circuits into Heathrow!)

One reason you'd never fly to Heathrow is the $3500 landing fee.

VFR or IFR? And you received the clearance to join the left traffic pattern RWY 9L from where? Entering from which direction? And where did you receive the clearance, VATSIM or IVAO? :D

Related

The instruction to join a "left downwind" is used to clear an aircraft into a standard traffic pattern with lefthand turns. The word "left" could be omitted, as only right turns and righthand traffic patterns are called with "right". In the case of EGLL - London Heathrow the standard pattern would be a northern traffic pattern for runways 09L/09R and a southern traffic pattern for runway 27L/27R.
If you should come to the unlikely situation that you are VFR and want to depart from Heathrow, the clearance to leave the CTR in a northerly direction would be best executed leaving the crosswind, but clarification on frequency never killed anybody:
A: Heathrow Tower, G-ABCD, request leave CTR direct northbound after crosswind 09L.

or
A: Heathrow Tower, G-ABCD, request heading 360 after turning crosswind 09L.

When departing an aerodrome with traffic, it is unwise to leave the CTR along the extended centerline/upwind, as you are impeding other traffic, especially in slower aircraft.


text:
How to find total climbing time based on Rate of Climb?
I am unsure on how to solve this problem. The only clue i have is to integrate ROC to find time.
A jet aircraft has the capacity to fly at an absolute altitude ceiling of 11000 m,
and a rate of climb (ROC) at sea level of 20.87 m/s. Calculate the time to climb
from sea level to 8000 m. Assume a linear variation of the rate of climb with
altitude during the whole maneuver.

I guess you know the rate of climb and ask about the climb time. Maybe you want to update the question's title. For the climb speed, look no further than here.

The fastest way is an integration. If you plot the inverted climb speed over altitude like in the plot below, the area under the curve will give you the time to climb. I would suggest you calculate the climb speed at every 1000 m by rule of proportion — at sea level it is 20.87 m/s and at 11.000 m it is 0 m/s. Then you get a plot like the one below. The red circles are the calculated points; the lines between them are straight interpolations.
Since the unit on the Y-axis is seconds per meter and the unit on the X-axis is meters, the area is in seconds. Just calculate the area of each trapezoid between the start and the end altitudes and add them. In the figure below I have crosshatched the trapezoids between 3000 m and 8000 m.

Inverted climb speed over altitude plot. Caution — this is a generic plot I did for this purpose earlier, so it uses different numbers. I crosshatched the area between 3000 m and 8000 m, because I made the plot for calculating the climb time from 3000 m to 8000 m.

In general, you need to integrate. But in this particular problem, the rate of climb goes down linearly, so the integration is trivial. At sea level the rate of climb is 20.87 m/s. At 11,000 ft. It's 0. So it goes down by 20.87/11 m/s (1.90) for each thousand feet of climb. The rate of climb at 8000 ft. would be 20.87 - 8*1.90, which is 5.6 m/s. The other nice thing about it being linear is that you can use the average rate of climb. That's (20.87 + 5.6) / 2, which is 13.24. At 13.24 m/s, climbing 8000 m will take 8000/13.24, which is 604 seconds, or just over 10 minutes.


text:
Have there been instances where a LSA manufacturer has been audited?
In theory, the authority to approve an LSA manufacturer and design has the right to audit their testing and work. What I'm interested in how often does this happen in practice, and whether there have been any cases of violations found because of this. Is the system of trusting manufacturers to be honest with their paperwork working so far?

Per this letter it appears that manufacturers who make LSA compliant aircraft are subject to a sort of enforced self regulation.  Basically, they are required to audit themselves every year and are told that the FAA could come and inspect their facility at any given moment, with heavy fines if an inspection is failed.
On top of this each aircraft itself is inspected by a technician before it leaves the facility to make sure that each aircraft meets the standards.
(The entire process is explained in more detail here.)
I did a bit of a search over a few of my favorite LSA news sites and I couldn't find any instances where an FAA inspection actually resulted in the proposed fines/punishments.  It seems that so far the semi-self-regulation model is working fairly well.  Well enough that, as Dan Johnson points out in that second article, it appears the FAA is considering using the same certification model for type aircraft as well.
To summarize, yes they are being audited, but by themselves.  It is also likely that outside bodies are auditing them as well, but nothing newsworthy seems to have come of any random inspections, so there is no mention of said audits.  I'm sure if somebody fails one, it will be big news.


text:
How do you start a jet engine if the start valve is stuck closed?
I was recently on a flight aboard an Airbus A380 where the flight was delayed 2 hours. The reason was claimed to be a start valve fault on engine #4, where it was stuck closed. According to the captain, they were able to get the engine started after manually starting the engine at the gate. How does this work?

Perusing the A380 Training Guide, Edition 01, 01 Sep 2008, Section 5 - Engine Starts, Subsections 5.8.6 (Engine Start Valve Stuck Closed),

5.8.6 Engine Start Valve Stuck Closed

ECAM actions – ENGINE MASTER OFF.
Check MEL, and in conjunction with, advise LAE of situation in preparation for Start Valve Manual Operation.
For Start Valve Manual Operation on Engines #2 and #4, the adjacent engine (if already running) will require shutdown, to enable LAE’s
  access to the manual start override procedure on the port side of the
  affected engine.
As the CAB Pb on the RMP is common to the Cockpit, Ground and Cabin Crew, advise the Cabin Crew to refrain from using the Cabin Interphone
  during the procedure.
When ready, accomplish normal engine start sequence:
  a)    Engine Start Selector to IGN/START.
  b)    Engine Master Lever to ON.
  c)    Command LAE to OPEN START VALVE AND KEEP OPEN.
  d)    At 50%N3, command LAE, START VALVE CLOSE.
  e)    Monitor engine parameters closely until stabilized.
Advise Cabin Crew upon completion of procedure.
In flight, only windmilling start will be available.

Glossary (correct if needed, please):
ECAM = Electronic Centralised Aircraft Monitor
LAE = Licensed Aircraft Engineer
CAB = Cabin
Pb = Pushbutton
RMP = Radio Management Panel
IGN = Ignition
N1/N2/N3 = N1 is LP (Low Pressure stage), N2 is IP (Intermediate Pressure stage), N3 is HP (High Pressure stage)
MEL = Minimum Equipment List

ECAM will display "ENG MASTER X ........ OFF" (X will be the engine with stuck valve)
(A320 display, only shows two engines, instead of four) (The message will appear in the lower left quadrant.)
Check the Minimum Equipment List (MEL) to determine if loss of engine is GO, GO IF, or NO GO, if failure is not in the MEL, it is classified by default as NO GO. Advise the on-site Licensed Aircraft Engineer (LAE) of the warning message in preparation for completing the Start Valve Manual Operation procedure.
If the engine with the stuck valve is #2 (left side inboard) or #4 (right side outboard), the adjacent engine will be required to be shutdown before commencing the manual start procedure. (This is because the engineer has to access the left side of the engine and for safety's sake the other engine, which would be gehind him must be shut down. If the fault is on the left outboard (#1) then the engineer would be on the far side of the engine from the #2 so #2 does not need to be shutdown.)
Since the Cabin Pushbutton (CAB Pb) on the Radio Management Panel (RMP) is common to the Cockpit, the Cabin Crew area AND the Ground circuit, the pilot should advise the Cabin Crew to not use the Cabin Interphone during the procedure. (If the pilot and the engineer are discussing starting the engine (or not) they don't want a flight attendant to be talking about starting pre-flight stuff at the same time, if the engineer heard the word start, he might wrongly assume it was the pilot.)
When pilot and engineer are ready, begin the normal engine start sequence with changes:
a) Turn the Engine Start Selector to IGN/START. (This is a panel from an A320, so only two engines are shown.)
b) Flip the Engine Master Lever (For the faulted engine) to ON. (This is a panel from an A320, so only two engines are shown.)
c) Over the interphone, command the engineer to manually open the start valve and keep it open. (I haven't yet looked for and found a schematic for an example engine, sorry. As shown in other diagrams/answers, it might be a socket wrench, etc.)
d) Watch the Engine Warning Display. (Again, A320, only two engines.) (This is an A380, showing N3) Once N3 is spun up to 50%, over the interphone, command the engineer to manually close the start valve.
e) Monitor the engine parameters closely until all are properly stable.
f) After the engineer has closed up the engine and vacated the area, start the other engines, if one was shut down per step 3.
Over the cabin interphone, notify the cabin crew that the procedure is complete. ( so they can resume using the interphone if needed. )
If the engine failed in-flight and upon restart a stuck valve warning was shown, all of the above would not be possible. At that time, the only way to restart the engine would be to attempt a windmill start (using the flow of air through the engine to turn the engine), there are other procedures for that.

Also, I do not yet have the engine schematics to show what the LAE actually does.

And chance of you putting together a short version in normal english for those of us who don't speak "Commercial A380 Pilot"-ese?

Not so short, but....

On the 747 with P&W engines at least, there was a procedure where a mechanic could manually open and close the start valve at the engine if energizing the start valve from the cockpit failed. Obviously you had to have communication with the mechanic to tell him when to close it. I never had to do it for real, and only a few times in the sim.

Wouldn't it be safer to just get a different craft?  It seems like if it's having that problem on the ground it might have it in the air, which would be problematic, no?

@JayCarr Once running the engine is self-sustaining: If you keep feeding it fuel and air it will keep making power (a cross-bleed start valve stuck closed is akin to the starter motor failing on a piston plane: If you can hand prop it and get it going it'll run fine - it's just annoying to have to start it that way). Should the engine fail in flight for some reason jets can usually be restarted without the need for cross-bleed power (the airflow through the engine will spin the turbine up).

@voretaq7 Oh, right, I keep forgetting about that whole "500mph wind flowing through the engine" bit :D.

@JayCarr Airlines typically don't have a spare aircraft on hand, they try to arrange it so that all aircraft are working, and if they did they probably would want to keep a reserve aircraft for something more serious than just a failed start valve. Also, the cost and time delay of ferrying another to a remote station would be cost prohibitive.

@voretaq7 Windmill starts are not as reliable as some people would think. It can be difficult to get enough airflow through the turbine to spin it up. The pilots of Pinnacle Airlines Flight 3701 didn't get their airspeed high enough (pilot error). My company flight tested a Citation CJ1+ and we were unable to achieve a windmill start at all even with proper airspeed/altitude out of the book. Enough to make me think twice about considering an unassisted air start an "assured thing."

To expand a little on this. Some start valves have an override that requires a tool, for example a 3/8 drive ratchet (First picture). While others use a push button to override the normal electrically operated solenoid (Second picture).
Here's an accident report of what happens when it all goes wrong.

great link, makes for some good reading.

The short answer is that there is a hole in the engine nacelle, which is the housing that you see around the engine. The mechanic sticks a tool, usually a 3/8" socket extension attached to a ratchet wrench though the hole and into a receptacle on the starter valve. They would then turn the wrench and override the stuck valve. The pilot can then go through the typical startup procedure. The process is the same for any of the engines, however, for the safety of the mechanic, an adjacent engine may need to be shut down.

Welcome to AV.se!


text:
Is a full traffic pattern required when there is no traffic at an untowered airport?
If there seems to be very little traffic at an untowered airport, and no one's replied to any of your radio calls, is it acceptable to just fly a straight-in approach to the runway, or should you still fly the full traffic pattern to final? It just seems like it would be a waste of time and fuel when it's not really necessary. Is there anything wrong with doing so?

I'd like to answer your question with a short example. A few days ago I flew to Venice (untowered) and decided to make a teardrop entry to set up for the 45. My calls were 10 and 5 miles out, both ending with "any traffic please advise." Guess what I saw overtaking me on my 4 o'clock position only a few hundred feet away at same altitude (500 feet above pattern)?
It is legal to make a straight in, but before you think about the time or fuel you waste please think about your own and even the guys who's not on CTAF and obviously heads down safety.
If you fly the 45 and the continue the pattern (it's not always left, check your sectional and the A/FD) everybody knows what the other one is doing and if necessary can act accordingly.

You should never use the phrase "any traffic please advise".  That is not recommended and can contribute to multiple people simultaneously stepping on each other on the radio.  You should just listen and monitor for the periodic broadcasts of others. See http://www.faa.gov/air_traffic/publications/atpubs/aim/aim0401.html -- Pilots stating, “Traffic in the area, please advise” is not a recognized Self-Announce Position and/or Intention phrase and should not be used under any condition.

You are right with what you're saying, but lets think about what's happening out there: A student pilot with his instructor is doing many traffic patterns at the same field, after the third pattern he maybe only annouces when hes turning base, after the fith he only keeps listenig on CTAF and after the seventh...? I already called 10 miles without adding this phrase at 5 miles I've addid it and gues what, there was one in the pattern.

It's not wrong, honestly absolutely right what you are saying but consider, sticking to all roules works perfectly out, but only if everyone does it. Now I ask you, does everyone stick to every rule. Let's dont blame others, let's imagine our selfs, if I would have a recording of my last flight (it even was a check ride) and the AIM beside and I would look everything up, i will honestly find more then one point where I, maybe not even violated a rule, but lets say deviated from the sugested way.

Well, the people who won't speak up when they hear another airplane announcing that they are entering the pattern, probably won't speak up just because you told them to either.

See AC 90-66A - RECOMMENDED ‘STANDARD TRAFFIC  PATTERNS AND PRACTICES FOR AERONAUTICAL OPERATIONS AT AIRPORTS WITHOUT OPERATING CONTROL TOWERS  for information about uncontrolled airport traffic patterns.
It includes the following which says that while the FAA recommends using the full pattern, it is not required:

7. GENERAL OPERATING PRACTICES.
a. Use of standard traffic patterns for all ‘aircraft  and CTAF procedures by radio-equipped aircraft  are
  recommended at all airports without operating  control towers.
  However, it is recognized that other  traffic patterns may already be
  in common use  at some airports or that special circumstances or
  conditions exist that may prevent use of the standard  traffic pattern

And then:

e. The FAA encourages pilots to use the standard  traffic pattern.
  However, for those pilots who choose  to execute a straight-in
  approach, maneuvering for  and execution of the approach should be
  completed  so as not to disrupt the flow of arriving and  departing
  traffic. Therefore, pilots operating in the  traffic pattern should be
  alert at all times to  aircraft executing straight-in approaches.
f. Pilots who wish to conduct instrument  approaches should be
  particularly alert for other aircraft in the pattern SO as to avoid
  interrupting  the flow of traffic. Position reports on the CTAF
  should include distance and direction from the  airport, as well as
  the pilot’s intentions upon completion of the approach

This is definitely a case of "What is legal is not always safe" -- absent good reason to do otherwise you should generally fly the standard pattern (or as is my preference, this pretty common variation that includes an overhead pass)

@voretaq7: Well, depending on your type of flying, you may very often be flying an instrument approach which is going to put you on a straight-in approach....  Especially if you are IFR, you don't want to tie up the airspace any longer than you need to either.

True - instrument approaches would definitely be an good reason for an exception to the "fly the pattern" rule.

Nobody on the radio does NOT mean no traffic.  You have IFR Arrivals not yet released by approach to tower frequency, and you have 100% legal no radio aircraft.  Fly the pattern so that they know where to look for you!

It is legal. The left downwind pattern entry at a 45 degree angle is recommended in the AIM to standardize operations and is therefore not regulatory in nature. However, the reason it's not a particularly good idea is that not all aircraft are required to have radios at a non-towered airport.
A traffic pattern is quite small compared to the en route phase or an instrument approach, there's not much time or fuel to be wasted.

I believe it is only illegal if you go the wrong direction in a traffic patter under vfr.

It is recommended in the AIM and elsewhere that you use the traffic pattern. However, the FAR requires only that you make any turns in the proper direction, not that you fly the pattern or enter the pattern on downwind. Straight in approaches are not prohibited. (91.126)
"Unless otherwise authorized or required, each person operating an aircraft on or in the vicinity of an airport in a Class G airspace area must comply with the requirements of this section.... When approaching to land at an airport without an operating control tower in Class G airspace... Each pilot of an airplane must make all turns of that airplane to the left unless the airport displays approved light signals or visual markings indicating that turns should be made to the right, in which case the pilot must make all turns to the right;"
"Otherwise authorized or required" applies to circling approaches, in which turns may be made in any direction (opening up a whole new set of risks).
Safety and common sense may dictate that you fly the pattern as a matter of practice. It is also safer to announce your position, and to announce "left (or right) downwind" and "left (or right) base", in case you or the plane you don't see happens to be going the wrong direction.

Per AOPA legal team regarding 91.126:
http://www.aopa.org/News-and-Video/All-News/2011/May/1/Pilot-Counsel.aspx   "So, while a straight-in approach to a runway at a nontowered airport is legal under the FARs, the straight-in approach must be started some considerable (but undefined) distance from the runway and the traffic pattern to be valid, and it must not interfere with aircraft in the traffic pattern or on an instrument approach"

I had forgotten about that until you posted it -- a 737 pilot, if I remember right, had his license suspended for a 3-mile final after a right turn.

There are a few airports out there with this line in their AF/D page:

STANDARD TFC PATTERN REQUIRED OF ALL ACFT.

Such as KMBT, as seen here.
Not sure how legally binding this is, but it is written.

Are there any small, uncontrolled fields that have that requirement? Murfreesboro is uncontrolled, but there's a relatively large amount of traffic there for an uncontrolled field, due to the flight school at MTSU.